This invention relates to planetary transmissions of the type disclosed in U.S. Pat. No. 3,540,311 granted Nov. 17, 1970 to C. W. Chillson. This prior patent discloses a planetary transmission in which the planetary elements are not provided with the usual support bearings which constrain the planetary elements against radial and tilting movements and instead, each of the planetary elements of the transmission include a plurality of axially-spaced gears which are so spaced along the spindle of their planetary elements that the net turning moment exerted by the input, output and reaction forces tending to tilt said element out of its radial plane is substantially zero. In addition, floating rings having rolling contact with the spindles of the planetary elements are provided to constrain the planetary elements against the radial forces thereon. Such a transmission is herein called a free-floating planetary transmission.
As described in said prior patent, such free-floating planetary transmissions have numerous advantages including the provision of a high speed ratio reduction at a substantial savings in weight over conventional planetary transmission. Applicant's assignee has built and successfully operated free-floating transmissions capable of transmitting as much as 750 horsepower.
The transmissions disclosed in said prior Chillson patent are not readily suitable for use with a plurality of independent power inputs, for example, for a marine propulsion transmission for providing a substantial speed-ratio reduction between a pair of side-by-side power units and the propeller system, and in which each power unit has an in-line connection with the transmission.
Said prior Chillson patent (FIG. 18) discloses a free-floating planetary transmission having co-axial, contra-rotating dual output shafts. However, with the configuration shown in this prior patent, the torque division between the two output shafts must be known in order to properly space the planet gears so that the net tilting moment on the planetary elements is zero. For example, in lines 54-55, column 16 of said Chillson patent the output torques of the two shafts are assumed to be equal. Obviously, however, when the output shafts are connected to dual helicopter propellers or to dual marine propellers, it is not possible to design the propellers for precisely equal load absorption. Hence, in the Chillson contra-rotating dual output configuration it may not be possible to achieve substantially zero tilting moment on the planetary elements. Because of the absence of normal support bearings for the planetary elements of a free-floating, planetary transmission, any significant tilting moment on the planetary elements would result in excessive stresses in the gear teeth of the planetary elements.